Ligand effect of gold colloid in the preparation of Au/Nb2O5 for CO oxidation

• Published in: Journal of catalysis Vol. 389; pp. 9 - 18
• Main Authors: Lin, Mingyue, Mochizuki, Chihiro, An, Baoxiang, Honma, Tetsuo, Haruta, Masatake, Ishida, Tamao, Murayama, Toru
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.09.2020
• Subjects: Alkanethiolates; CO oxidation; Gold nanoparticles; Niobium oxide; Niobium oxide; CO oxidation; Alkanethiolates; Gold nanoparticles
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2020.05.014

[Display omitted] •Au/Nb2O5 catalysts were synthesized using thiolate-protected gold colloid.•Highly active Au/Nb2O5 for CO oxidation was obtained (100% conversion less than 25 °C).•Effect of remaining sulfur species on the preparation of Au/Nb2O5 was investigated.•Effect of remaining sulfur species on the catalytic activity was investigated.•Small amount of remaining sulfur species is vital for small size of Au nanoparticles. Sol immobilization method by using a ligand-protected gold colloid precursor, Aun(SC12H25)m, was applied for the deposition of gold on Nb2O5 which is a typical solid acid. The effects of the thiolate ligand on the preparation of Au/Nb2O5 and on the catalytic activity for CO oxidation were investigated. Although most of the thiolate ligands were removed during the calcination at 300 °C, a small amount of sulfur species still remained on the catalyst, which played an important role for preventing the aggregation of the gold nanoparticles to give ca. 2.8 nm in a mean diameter with the gold loading amounts in the range from 0.9 wt% to 4.2 wt%. Calcination at a lower temperature (250 °C) gave a larger amount of the sulfur species than did the calcination at 300 °C, lowering catalytic activity for CO oxidation. The temperature for 50% CO conversion (T50%) was 3 °C for 0.9 wt% Au/Nb2O5 under 20,000 mL h−1 gcat−1 using 1 vol% CO in air. With an increase in the loading amount of gold, the catalytic activity became higher. The T50% of 4.2 wt% Au/Nb2O5 was −41 °C and turnover frequency (TOF) based on a number of the perimeter gold atom was calculated to be 8.7 s−1 at 20 °C. The TOF value obtained by Au/Nb2O5 prepared by deposition-reduction without thiolate ligands was 5.0 s−1. This result suggests that the sulfur remained on the catalyst did not inhibit CO oxidation.